Chemical-mechanical polishing (CMP) is performed in the processing of semiconductor wafers and/or chips on commercially available polishers. The standard CMP polisher has a polishing table carrying a circular polishing pad and a rotating carrier for holding the wafer. A slurry is used on the polishing pad.
Ideally, a CMP polisher delivers a global uniform, as well as locally planarized wafer. However, global uniformity on a wafer-to-wafer basis is difficult to achieve. Current pad designs include stacked pads in which an upper hard pad is stacked on a soft sub-pad which is disposed on a polishing platen associated with the polishing table. The hard pad may be, for example, an IC 1000 pad while the soft pad may be, for example, a Suba 4 pad. These stacked pads have functioned to improve polish uniformity. However, the stacked pads require the disposal of both pads after a certain number of wafers have been polished on the upper pad or if a sub-pad of differing compressibility is desired. It is known to replace the soft pad with a semi-permanent silicon pad of the same or similar compressibility as the Suba 4 soft pad. However, it is desirable to use a sub-pad of a material whose rigidity and pliability could be varied ex situ or in situ to achieve variable polish pad hardness.